Field of the Invention
The present invention relates to an ultrasonic sensor, a method of fabricating it, and an ultrasonic diagnostic device using such an ultrasonic sensor. More particularly, the invention relates to an ultrasonic sensor for collecting information that gives a measure of a health examination or care such as the thickness of an adipose layer within a living body or the elastic modulus of blood vessels. The invention also relates to a method of fabricating the ultrasonic sensor and to an ultrasonic diagnostic device utilizing the ultrasonic sensor.
Generally, when information about the interior of a living body (such as the thickness of adipose, the elastic modulus of blood vessels, or the shapes of blood vessels) should be collected using an ultrasonic wave, it is necessary to suppress reflections of the ultrasonic wave at the skin to permit the ultrasonic wave to propagate into the body efficiently. Therefore, an oily liquid, or jelly, is interposed between an ultrasonic sensor used in an ultrasonic diagnostic device and the skin. That is, the oily liquid is applied to the skin, and then the ultrasonic sensor is brought into intimate contact with the skin.
Where an oily liquid is applied to the skin, the application operation is cumbersome to perform. Also, another problem occurs, i.e., uncomfortableness such as stickiness is given to the examinee.
For this reason, ultrasonic diagnostic devices that do not need application of oily liquid to the skin have been proposed in recent years. A sensor used in such an ultrasonic diagnostic device (as disclosed in Japanese patent laid-open No. 289554/1995) is described below.
FIG. 22 is a cross-sectional view schematically showing the structure of an ultrasonic sensor 11 associated with the prior art ultrasonic diagnostic device. The ultrasonic sensor 11 comprises an ultrasonic oscillator 12 encased in a package 13 made of a metal or other material. The package 13 is provided with an opening window 13a in a location ahead of the ultrasonic oscillator 12. The opening window 13a is coated with an artificial chitinous film 14. The space sealed by the package 13 and the artificial film 14 is filled with silicone oil acting as an ultrasound transmission liquid 15 in which the ultrasonic oscillator 12 is immersed.
The ultrasonic oscillator 12 comprises oscillatory elements 16a and 16b. Any one of them is oscillated for transmission. An ultrasonic wave is sent into the living body from the opening window 13a. The other oscillatory element receives the ultrasonic wave reflected from inside the living body.
The artificial film 14 consisting of a component resembling the skin is used in the portion that is brought into intimate contact with the skin in this way. Consequently, the adhesion to the skin can be enhanced without using oily liquid, and no phase deviation occurs in the ultrasonic wave. As a result, it is not necessary to apply an oily liquid to the skin.
Generally, where an air layer exists between an ultrasonic oscillator and the skin, ultrasonic waves are attenuated by the air layer. This makes it impossible to obtain desired information. Accordingly, in the past, silicone oil has been injected into the package, and the opening window is covered by the artificial film as mentioned above. However, this has the following problems.
(1) If bubbles of air or the like are mixed into the silicone oil, ultrasonic waves are attenuated by the bubbles. Therefore, when the silicone oil is injected into the package, it is necessary to seal the package to prevent intrusion of bubbles. This makes fabrication difficult.
(2) To bring the artificial film into intimate contact with skin wrinkles or the like, it is necessary that the material of the film be comparable in softness with, or superior in softness to, the skin of the human body. If the package is closed using such a material, holes tend to be easily formed in the artificial film in use. Thus, the durability has a problem. Hence, it is difficult to use the film for a long time.
(3) Liquids such as silicone oil generally have high coefficients of thermal coefficient. During use, they expand, causing leakage of silicone oil or varying the path in which ultrasonic waves propagate. This makes it difficult to obtain precise information about the interior of a living body.
Accordingly, it is an object of the present invention to provide a high-sensitivity ultrasonic sensor that is contacted with the skin with improved adhesion without the necessity of sealing an oily liquid (jelly) or interposing the jelly between the skin and the ultrasonic sensor, as well as an ultrasonic diagnostic device using this ultrasonic sensor.
An ultrasonic sensor associated with an ultrasonic diagnostic device in accordance with the present invention sends out an ultrasonic wave into a living body by driving a piezoelectric element mounted on a substrate according to an input drive signal and receives the wave reflected from inside the living body. An intimate contact layer is formed on the top layer of the piezoelectric element and sticky against the skin of a living body. The ultrasonic sensor is sucked onto the skin of the living body via the intimate contact layer. This structure makes it unnecessary to seal silicone oil or the like. Furthermore, use of any special material is not necessary. An ultrasonic wave can be sent into and received from a living body efficiently without applying an oily liquid between the ultrasonic sensor and the skin.
An ultrasonic wave can be sent into a living body and the reflected wave from inside the living body can be received more effectively by using a material having a Young""s modulus ranging from 1.0xc3x97105 to 3.0xc3x97107 dyne/cm2 as the intimate contact layer.
Substances whose Young""s modulus ranging are in the above-described range, i.e., those materials which are preferable as the intimate contact layer, generally show poor adhesion to silicon-based resins, epoxy-based resins, and piezoelectric materials such as PZT. Therefore, the adhesive contact layer showing poor adhesion can be attached to the ultrasonic diagnostic device by giving a mechanism for holding the intimate contact layer to the ultrasonic diagnostic device. The adhesion of the ultrasonic diagnostic device to the skin can be improved. Also, the sensitivity in sending and receiving ultrasonic waves can be enhanced. Furthermore, the treatability can be improved.
A method of fabricating an ultrasonic sensor in accordance with the present invention comprises the steps of: mounting a piezoelectric element on a substrate; mounting an intimate contact layer-holding mechanism to the substrate; and injecting a resin that cures at room temperature, when heated, or irradiated with ultraviolet radiation into the intimate contact layer-holding mechanism and curing the resin. The intimate contact layer can be easily formed by this fabrication method.
An ultrasonic diagnostic device having an ultrasonic sensor is designed to comprise a storage portion for storing an output value when an initial detection is performed and a replacement time-informing portion for comparing information about a living body produced at the time of the initial detection with the currently detected information about the living body and for informing a user of the time when the intimate contact layer should be replaced if a given ratio of the output value (such as a voltage) indicating information about the living body at the time of the initial detection is reached. Consequently, it is possible that the user will be informed of the time when the intimate contact layer should be replaced. Hence, biological information can be measured stably for a long time.
The intimate contact layer can be so constructed that it does not touch the living body when the device is not in use. Alternatively, a protective layer that protects the intimate contact layer when the device is not in use is provided. In this way, the intimate contact layer with low strength can be protected. In consequence, it can be used stably for a long time.
Contaminants such as dust tend to adhere to the surface of members such as silicone gel which are sucked onto the skin of a living body. Therefore, the intimate contact layer is made detachable. If the intimate contact layer is contaminated with dust, it can be replaced with a new intimate contact layer. The ultrasonic diagnostic device can be used stably for a long time while maintaining the sensitivity of the device.